Nowadays, in the Global System of Mobile (GSM) network, mobile subscribers are able to roam among GSM networks of different operators, and the GSM networks can also implement access restriction to the mobile subscribers. Methods for implementing the access restriction in the GSM networks are very mature. One of the methods can obtain a Public Land Mobile Network (PLMN) number of a home GSM network of the subscriber by analyzing User Identifiers such as International Mobile Subscriber Identity (IMSI) or Mobile Station Integrated Services Digital Network (MSISDN) number. Since different operators have different PLMN numbers of their networks, this method can determine and obtain the home GSM network of the subscriber by the obtained PLMN number, accordingly, the corresponding access restriction can be implemented to the subscriber according to the home GSM network of the subscriber. A detailed implementation procedure includes:
If no roaming permission contract is subscribed between GSM networks of two operators, when a Mobile Station (MS) of a first GSM network roams into a second GSM network, the MS will initiate a Location Registration Request to the second GSM network. The second GSM network obtains the PLMN number of the home network of the MS by analyzing the user identifier of the MS, and then determines that the home GSM network of the MS is the first GSM network. Therefore, the second GSM network returns a Location Registration Reject Message, with a reason value of “the PLMN number is not permitted” to the MS. The MS writes the PLMN number in the reason value of the message in a list of “PLMN forbidden to access” in the Subscriber Identity Module (SIM) of the MS after receiving the reject message, wherein the list will still be saved in the SIM card when the MS is shut down or the SIM card is taken out of the MS; the MS can implement access restrictions by the list of “PLMN forbidden to access”. When the MS operates in a automatic PLMN network selection mode, if the PLMN number of the selected network is in the list of “PLMN forbidden to access”, the MS will not initiate the Location Register Request to the GSM network corresponding to the PLMN number, thereby the access restriction is implemented automatically; when the MS operates in a manual PLMN network selection mode, if the MS successfully accesses to a certain PLMN network, the MS will determine whether the PLMN number of the network exists in the list of “PLMN forbidden to access”, if it exists, the PLMN number will be deleted from the list of “PLMN forbidden to access”, so that the MS is able to initiate the Location Register Request to the PLMN network in the automatic PLMN network selection mode. By the list of “PLMN forbidden to access”, the method can automatically forbid the MS to initiate the Location Register Request to the PLMN network which is forbidden to access, so the demand for access restriction is satisfied.
However, with the emergence of the 3rd Generation (3G) networks, such as Wideband Code Division Multiple Access (WCDMA), the above-mentioned method cannot satisfy the demand of access restriction. For instance, some operators may simultaneously have a GSM network and a WCDMA network, and the GSM network and the WCDMA network can respectively have their own PLMN numbers or share the same PLMN number. If they share one PLMN number, the GSM network and the WCDMA network cannot be differentiated according to the PLMN number, therefore it is impossible to implement the access restriction of the GSM network or the WCDMA network. Similarly, as for networks of other types, the above-mentioned problem still exists.